Various multi-channel audio rendering systems such as 5.1, 7.1 or 9.1 multi-channel audio rendering systems are currently in use. The multi-channel audio rendering systems allow for the generation of a surround sound originating from 5+1, 7+1 or 9+1 speaker locations, respectively. For an efficient transmission or for an efficient storing of the corresponding multi-channel audio signals, multi-channel audio codec (encoder/decoder) systems such as Dolby Digital or Dolby Digital Plus are being used. These multi-channel audio codec systems are typically downward compatible in order to allow a N.1 multi-channel audio decoder (e.g., N=5) to decode and render at least part of an M.1 multi-channel audio signal (e.g., M=7), with M being greater than N. More particularly, the bitstreams generated by the multi-channel audio codec systems are typically downward compatible in order to allow a N.1 multi-channel audio decoder (e.g., N=5) to decode and render at least part of an M.1 multi-channel audio signal (e.g., M=7). By way of example, an encoded bitstream of a 7.1 multi-channel audio signal should be decodable by a 5.1 multi-channel audio decoder. A possible way to implement such downward compatibility is to encode a M.1 multi-channel audio signal into a plurality of substreams (e.g., into an independent substream (hereinafter referred to as “IS”) and into one or more dependent substreams (hereinafter referred to as “DS”)). The IS may comprise a basic encoded N.1 multi-channel audio signal (e.g., an encoded 5.1 audio signal) and the one or more DS may comprise replacement and/or extension channels for rendering the full M.1 multi-channel audio signal (as will be outlined in further detail below). Furthermore, the bitstream may comprise multiple IS (i.e., a plurality of independent substreams) each having one or more associated DS. The plurality of IS and associated DS may, for example, be used to carry a plurality of different broadcast programs or a plurality of associated audio tracks (such as for different languages or for directors comments, etc.), respectively.
The present document addresses the aspect of an efficient encoding of a plurality of substreams (e.g., an IS and one or more associated DS or a plurality of IS and respective one or more associated DS) of a multi-channel audio signal.